Reclamation processing of polyvinyl chloride-scrap materials and products produced thereby

ABSTRACT

Recompoundable polyvinyl chloride suitable for reuse, for example, in cable and wire production is recovered from a scrap material which includes plasticized polyvinyl chloride. A charge of plasticized polyvinyl chloride scrap material is treated with a solvent to form a solvent mixture with one component thereof being a solvent solution of dissolved vinyl chloride polymer and plasticizers. The mixture is heated and agitated and scrap metal and other gross solids, if present, are removed. Then the solvent mixture is treated with an acid which advantageously causes a flocculation of suspended insolubles such as pigments and fillers. Except when using cyclohexanone as the solvent, the treatment with the acid must be accomplished, unexpectedly, in the presence of an additional flocculating agent. Suitable floccuating agents include liquid monomeric esters, which are effective only for cable and wire scrap, polystyrene, polymethyl methacrylate, poly (vinyl isobutyl ether), polyvinyl acetate and ethylene vinyl acetate, the latter acetate being effective only for scrap plastic such as extruder purgings.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to reclamation processing of vinyl chloridepolymer-containing materials and, more particularly, to methods of andapparatus for separating and recovering a recompoundable vinyl chloridepolymer, particularly polyvinyl chloride (hereinafter PVC), from apolymeric scrap material, and to a recompoundable PVC resultingtherefrom.

2. Description of the Prior Art

Scrap material including metal components generated during manyindustrial processes has for years been reprocessed to recover the metaltherefrom. Copper, for example, has been recovered from telephone cableswhich have been scrapped at some stage of the manufacturing process.Telephone cables which have been removed from service have likewise beenreprocessed. The residue from prior art metal reclaiming processes hasincluded middlings of textile, plasticizers, pigments and fillers aswell as a basic insulating plastic compound such as PVC. Only limiteduse has been found for this residue, as such, and to date the residuehas not been convertible economically into its individual components.

The residue has been disposed of by incineration or used as land fill.Ecological considerations now require more desirable disposalprocedures. Moreover, economic factors similar to the high cost anduncertain supply of copper which have historically justified copperreclaiming, have come to apply to polymers and plasticizers underpresent international market conditions.

Recent industry efforts have been made, for example, to reclaim PVC forre-use. In general, it is well known that solvent recovery techniquescan be employed for dissolving both PVC and associated plasticizers,which together are the major weight fraction of the nonmetalliccomponents of scrap telephone cable. In this approach, the metal isreadily separated, and the nonmetallic components can thereafter berecovered.

The published prior art (See, for example U.S. Pat. No. 3,836,486.)includes treating a scrap charge, which includes a plasticized PVCcomposition with a solvent, such as, for example, tetrahydrofuran,cyclohexanone or methylethyl ketone, to form a solvent mixture. Thesolvent mixture is then treated with a nonsolvent for PVC to precipitateout and separate a PVC composition from plasticizers, solvent andnonsolvent which are recovered subsequently for reuse.

The products recovered from the above-described process will vary incomposition depending on the quantity of other soluble or suspendableparticulate matter, such as plasticizers, flame retardants, fillers, andpigments, which were present in the original scrap charge. Where scrapmaterial from a variety of sources is used, variations in the componentsof the scrap material are not readily controllable at the process input.

The PVC composition recovered by the above-mentioned process undesirablyincludes components, such as pigments and fillers, which would cause therecovered PVC to be unsuitable for use in insulating wires and cableswhere color coding is a consideration. In order to recover a PVC whichis readily reusable in the wire and cable industry, a recovery processmust include the capability of separating pigments and fillers, andother additives as well as the plasticizers, from the scrap material sothat an essentially pure PVC resin is obtained.

In U.S. Pat. No. 3,043,785 a pigmented polymeric composition isadvantageously depigmented by a process which includes dissolving thepigmented polymeric composition in a suitable nonreactive waterinsoluble organic solvent. A water-soluble cellulose ether isincorporated in an aqueous phase which is then mixed with the resultingorganic solution containing a dispersed pigment to accelerate pigmentsettling, the cellulose ether facilitating flocculation of the pigment.Then the organic polymer solution is separated from the pigment and theaqueous phase advantageously by settling the organic polymer solutionfrom the aqueous phase, separating the organic polymeric solution fromthe aqueous phase, filtering the separated polymeric solution, andsubsequently isolating and recovering the reclaimed and depigmentedpolymer. See also U.S. Pat. No. 2,915,482.

The prior art also shows a polyethylene carbon black mixture dissolvedin an organic solvent and the addition of a strongly acidic coagulantsuch as hydrochloric acid after which the mixture is refluxed. See U.S.Pat. No. 3,232,891.

SUMMARY OF THE INVENTION

In accordance with the principles of this invention, a process forrecovering an essentially pure vinyl chloride polymer from a scrapmaterial which comprises plasticized PVC and additives insoluble inparticular solvents, includes the steps of contacting the scrap materialwith a solvent for vinyl chloride polymers to form a solvent mixturecomprising a solvent solution of dissolved polyvinyl chloride andsuspended particulates, treating the mixture with at least an acid toflocculate and remove the suspended particulates and treating thesolvent solution with a non-solvent to selectively precipitateessentially pure vinyl chloride polymer therfrom.

More particularly, scrap material which includes, for example,plasticized PVC is dried and then contacted with a well known solventfor vinyl chloride polymers and plasticizers such as, for example,methyl ethyl ketone to form a solvent mixture comprising a solventsolution of dissolved vinyl chloride polymers and suspendedparticulates. The solvent mixture with copper and other gross solidcomponents thereof is then passed through a separator where the copperand other gross solids are removed.

The solvent mixture is then passed through a flocculation tank whereinan acid, such as hydrochloric acid, is added in order to flocculate andprecipitate the suspended particulates such as pigments and fillers.Following the addition of the acid, calcium hydroxide is introduced toaccelerate the flocculation and to neutralize the acid. Except whenusing cyclohexanone as the solvent, the treatment with the acid must beaccomplished in the presence of a suitable supplementary flocculatingagent which generally must be added to the solvent mixture prior to theaddition of the acid.

A suitable supplementary flocculating agent has been found to bepolymeric materials such as polystyrene, polymethyl methacrylate, poly(vinyl isobutyl ether) and polyvinyl acetate. A liquid monomeric estersuch as, for example, ethyl acetate has been found to be a suitableflocculating agent in reclamation processing of scrap materialcomprising scrap conductors and cables. Ethylene vinyl acetate has beenfound to be a suitable flocculating agent for scrap plastic such asextruder purgings.

Then the solvent solution containing the plasticized PVC is treated witha non-solvent for the PVC, for example, methanol, to precipitate out ofthe solution an essentially pure PVC resin. The solvent and thenon-solvent are selected to be miscible with each other. The resultingmixture of a solution of plasticizer, solvent and non-solvent and thePVC precipitate is centrifuged with the PVC being separated and thendried. The PVC is suitable for recompounding and reuse in wire and cableproduction. The solution comprising the solvent and non-solvent togetherwith the plasticizer is moved through a water dryer and then to asolvent sill where the solvent and non-solvent are removed separatelyfrom the solution which is then further distilled to recoverplasticizers which also may be reused in subsequent processing.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and features of the present invention will be more readilyunderstood from the following detailed description of specificembodiments thereof when read in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a simplified flow diagram depicting and illustrating the stepsused in carrying out the principles of the method of this invention;

FIG. 2 is a detailed schematic flow diagram showing the sequence ofsteps as well as apparatus for carrying out the principles of thisinvention as depicted in FIG. 1; and

FIG. 3 is a graph showing the molecular weight distribution ofcommercially available virgin PVC and of the PVC resin recovered by aprocess which embodies the principles of this invention.

DETAILED DESCRIPTION

The present invention is described primarily in terms of steps of aprocess as illustrated in the flow diagram of FIG. 1 for recovering anessentially pure polyvinyl chloride (PVC) resin and other materials froma scrap charge. The process includes treating the scrap charge whichcomprises a vinyl chloride polymer composition with a solvent capable ofdissolving vinyl chloride polymers such as, for example, methyl ethylketone, hereafter designated as MEK, which has been heated to a suitabletemperature, typically approximately 80° C. Upon treatment, a solventmixture is formed comprising as one component thereof a solvent solutionof dissolved vinyl chloride polymer, dissolved plasticizers andsuspended particulates.

The solvent mixture is further treated in accordance with the principlesof this invention to flocculate the suspended particulates and to treatfurther the solvent solution to recover an essentially pure PVC resin.

Following the removal of the PVC, there remains a solvent solution whichincludes the solvent, nonsolvent and plasticizer. The solvent solutionis distilled to recover separately the solvent, the nonsolvent and theplasticizers.

The term "vinyl chloride polymer" is intended to include not onlyhomopolymers of vinyl chloride, that is PVC, but also thermoplasticcopolymers of vinyl chloride with one or more different monomers.

The terms "vinyl chloride polymer composition" or "PVC compound" areintended to mean one or more of such vinyl chloride polymers with one ormore of the additives normally present in vinyl compounds for wire andcable purposes and typically includes, for example, pigments andfillers. The composition may also contain other constituents such as,for example, stabilizers, emulsifiers, plasticizer compositions, waxes,fillers, ultraviolet absorbers and antioxidants.

The term "plasticizer composition" is intended to refer to a compositioncontaining a major proportion of a vinyl chloride polymer plasticizer,alone or in admixture with a minor amount of the vinyl chloride polymerand other ingredients usually present in the manufacture of articlesfrom vinyl chloride polymers such as stabilizers, emulsifiers, butexcluding essentially all pigments and fillers.

The term "scrap material" is intended to mean a scrap conductor havingan insulation which comprises a vinyl chloride polymer composition, theconductor covering also possibly including other constituents such as,for example, textiles, and also is intended to mean a scrap plastic orscrap which is essentially a vinyl chloride polymer composition, suchas, for example, that found in extruder purgings.

It should be understood that cross-linked PVC compositions are notdissolved by the process embodying the steps of this invention.Cross-linked compositions are defined as those in which a PVCcomposition includes a cross-linking agent, e.g., tetraethylene glycoldimethacrylate, TEGDM, which when treated with chemical or electricalradiation causes an interlocking of the molecules.

Referring now to FIG. 2, there is shown an apparatus designatedgenerally by the numeral 20, for carrying out the steps of the flowdiagram shown in FIG. 1 for recovering PVC and additives from a scrapvinyl chloride polymer composition.

A charge of scrap material consisting of PVC-compound-insulatedconductors, PVC-compound-jacketed cable, or other PVC-containingmaterial is introduced into a hopper 21, and cut by a chopping apparatus22 into portions conveniently about one quarter inch to approximatelysix inches in major dimension. This maximizes the available surface areaper unit of scrap thereby promoting rapid dissolution.

It should be understood that while this description involves recoveryfrom a scrap-conductor, scrap material, that the principles of thisinvention are not confined to treating a scrap charge which includescopper or other gross solids but are equally applicable to treating aPVC composition of matter such as may be found, for example, in extruderpurgings.

Typically, field scrap-conductor, scrap material is comprised of 63% byweight of copper, 7% textile, 18% PVC resin, 7% plasticizer and 5% otheradditives. The copper content of manufacturing scrap-conductor, scrapmaterial is in the range of 75 to 80% by weight.

The chopped scrap material is discharged onto a feeder, such as aconveyor belt, and thence through a dryer 24 which may be, for example,steam heated to remove moisture. The dried chopped scrap material isthen moved into a solution tank 26. C.,

Dissolution of the chopped PVC scrap material occurs in the solutiontank 26 where the scrap is contacted by a suitable solvent for vinylchloride polymers to form a solvent mixture which includes as onecomponent thereof a solvent solution of dissolved vinyl chloride polymerand plasticizers. A suitable solvent includes, for example, MEK,tetrahydrofuran (hereinafter "THF"), dimethyl formamide (hereinafter"DMF"), and cyclohexanone. Preferably, MEK is employed. The solvent isadmitted to the solution tank 26 along a line 27 from a storage source28 where it is advantageously preheated to the boiling point of thesolvent, which for MEK is 79°-80° C, by a heater 29.

When MEK is the solvent, the temperature in the tank 26 is preferablymaintained by an external heater 31 through steam jacketing, forexample, above room temperature and preferably between 70°-80° C.However, when the solvent employed comprises THF or cyclohexanone, thetemperature may be maintained at room temperature. Preferably,agitation, provided by an agitator 32, is used to promote thedissolution of the PVC.

At this time, the tank 26 includes the solvent treated scrap materialand the resultant solution containing dissolved vinyl chloride polymer.As the PVC and associated plasticizers are dissolved in the MEK, thesolution viscosity may be monitored by a controller 33 and MEK is addedautomatically by action of a feedback loop (not shown) and a valve 34 toinsure that the material in the tank 26 does not gel. For efficient useof the solvent, it has been found that the resultant solution shouldpreferably contain at least about three percent by weight of the vinylchloride polymer.

One of the important aspects of this invention is the capability ofremoving contaminants such as pigments and fillers, for example, fromthe solvent mixture to facilitate the recovery of essentially pure PVCreadily recompoundable for reuse in wire and cable manufacturingprocesses. In order to accomplish this as disclosed in application Ser.No. 670,469 filed of even date herewith in the names of B. Broyde et al,a flocculation of the pigments and fillers is caused to occur. Thelast-identified application disclosed that, unexpectedly, theflocculation is accomplished by contacting the solvent mixture with anacidic constituent. Further, it was found that except when usingcyclohexanone as the solvent, an acid will flocculate out thecontaminants only in the presence of a supplementary flocculating agentwhich is dissolved by the PVC solvent and which is insolubilized by theacid on refluxing. In this way, the supplementary flocculating agent,for example, cellulose acetate, would come out of the mixture togetherwith the pigment and filler contaminants.

Polymeric materials were later found to be suitable supplementaryflocculating agents for both scrap plastic and scrap conductor scrapmaterials. This is somewhat surprising in that the PVC material is apolymeric material which is not intended to be brought out of themixture with, for example, the pigments and fillers. A furthercharacterization of the polymeric material, which is suitable as asupplementary flocculating agent, as being one which is insolubilized byan acid on refluxing distinguishes the PVC.

Further, it was later found that when processing scrap conductor scrapmaterial, a liquid monomeric ester has been found to be a suitablesupplementary flocculating agent. Suitable liquid monomeric estersinclude, for example, ethyl acetate, propyl acetate, isopropyl acetate,isoamyl acetate, pentyl acetate, butyl acetate and a mixture comprisingany of the foregoing acetates.

The effectiveness of the above-listed low molecular weight esters asflocculating agents appears to constitute a surprising result. Thehydrolysis of butyl acetate, for example, in the presence of the aqueousacid results in acetic acid and butyl alcohol. Since acetic acid andbutyl alcohol are each soluble in MEK, for example, it would not beexpected that they would flocculate out. Moreover, acetic acid in and ofitself as a constituent has been added to the solvent and has not causedan effective flocculation.

Equally surprising is the result that the liquid monomeric esters causeflocculation in scrap conductor scrap material mixtures but not in scrapplastic scrap material mixtures. It would seem that since the suspendedparticulates are common to both scrap materials that flocculation shouldbe caused by the liquid monomeric esters in both.

Still further, it has been found that flocculation of pigments andfillers in a scrap plastic scrap material is caused to occur by theaddition of ethylene vinyl acetate (EVA) as the supplementaryflocculating agent prior to the addition of the acid. The EVA copolymerhydrolyzes to ethylene alcohol copolymer and may cause flocculation bythe same mechanism as that associated with the cellulose acetate and asdisclosed in application Ser. No. 670,469 filed of even date herewith inthe names of B. Broyde et al.

It has also been determined that the supplementary flocculation agentmust be added to the solvent mixture prior to the addition of the acidunless the scrap includes a suitable amount of cellulose acetate, forexample, 1/10% by weight. Scrap wire containing cellulose acetate may beat the type, for example, disclosed in U.S. Pat. No. 3,668,302, issuedJune 6, 1972 in the name of D. E. Boland, and incorporated by referencehereinto.

The above described treatment may be required because viscosityincreases rapidly with concentration, and the time required toflocculate is a function of viscosity. On the other hand, the moreconcentrated the solution, the less distillation is required per poundof scrap and hence the better are the economics of the process. Theadvantages of a higher concentration while avoiding the disadvantageassociated therewith may be realized by using THF. However, THF isrelatively expensive.

There are advantages in using one of the herein before-mentionedacetates other than cellulose acetate. Since the acetates enumerated,other than cellulose acetate, are liquids, the acetates may be recycledthus eliminating or at least minimizing the replenishment thereof forthe treatment of subsequent batches. However, the use of acetates otherthan cellulose acetate may complicate the distillation step because of amore complex azeotrope formation.

At this time the solution component of the solvent mixture, comprisingsolvent and dissolved PVC, is clouded by colloidal material suspendedtherein. The colloidal material includes pigments, fillers and the like.

These conditions are maintained in the solution tank 26 for a timesufficient to achieve the desired degree of dissolution of the choppedvinyl chloride polymer composition. It has been found that when usingMEK as the solvent, each batch or change of scrap material typicallyshould remain in the solution tank for approximately one hour to producea 5% by weight vinyl chloride polymer solution.

Then the resulting solvent mixture which typically includes a solventsolution and residual undissolved solids, comprising principally metal,but also possibly including other polymeric insulating materials such aspolyethylene, polypropylene, crosslinked PVC, as well as rubber,synthetic or natural fibers, wood pulp and other relatively bulkyinsolubles, are passed through a vibrating screen separator 36.Alternatively, the solvent mixture may be admitted to a centrifuge (notshown). At this point, copper, textiles and other insolubles or "grosssolids" as they are often designated in the art are removed from thesolvent mixture by screening, passed through a dryer 37, and thendeposited in a collector bin 38. These components await conventionalsorting and ultimate refining of the copper and other gross solids.

The solvent mixture comprising a solvent solution which includesdissolved PVC, is cloudy and is discharged through a line 41 and into aflocculation tank 42. The flocculation tank 42 is also provided with anagitator 48 and facilities 43 for controlling the temperature of thesolvent mixture.

The insoluble particulate material entrained in the solution andadmitted to the flocculation tank 42 typically will include a variety ofmaterials used in PVC compounding. These include, but are not limitedto, lead salts such as, for example, a sulfate, carbonate, phosphite orphthalate, fillers such as calcium carbonate and calcined clay, flameretardants such as antimony trioxide, adsorbents such as activatedcharcoal and any badly degraded or crosslinked PVC which also isinsoluble in MEK. These insolubles are removed from the solvent mixtureby flocculation procedures pursuant to this invention.

It will be recalled that cellulose acetate, or any of the suitableflocculating agents disclosed hereinbefore, is added to the solventmixture preferably in the tank 26 prior to the removal of gross solidstherefrom by centrifuging. It has been determined that the supplementaryflocculating agent, which unexpectedly is required in forming a floc ofparticular constituents of the PVC composition except when usingcyclohexanone as the solvent, must be added to the solvent mixture priorto the introduction of an acid in order to minimize the solution time.

Additional amounts of the supplementary flocculating agent may be addedinto the tank 42 from a source tank 44 along a line 46 through a valve47. Optionally, all of the supplementary flocculating agent may be addedto the solvent mixture in the tank 42 prior to the introduction of theacid.

Then a measured amount of an acid such as nitric acid, sulfuric acid, orpreferably hydrochloric acid, from the supply 44 is added to the tank 42in the presence of the supplementary flocculating agent, for example,whereupon the suspended particulates are caused to flocculate andprecipitate. Specifically, the supplementary flocculating agent and anyclays, fillers, metal salts or insoluble pigments which are present areflocculated out of the solvent mixture. The temperature of the solventmixture is increased by the heater 43 to within generally the range of65° C. to reflux, e.g., 82° C., depending on atmospheric pressure, andis accompanied by agitation. The solution is allowed to remain warm forapproximately 15 to 30 minutes and agitated slowly for about ten minutesto allow flocculation to occur. In a preferred embodiment, the solventmixture in the tank 42 may be heated to reflux prior to the introductionof the acid.

It is speculated that the acid, e.g., hydrochloric acid, initiates theflocculation by rendering insoluble the supplementary flocculating agentand that coagulation of the particulate additives in the PVC scrapsolutions prepared in THF, MEK, DMF or cyclohexanone then occurs.

The hydrochloric acid, added to the solvent mixture, causes flocculationof essentially all pigments, fillers and the like which are included inthe scrap charge. The floc advantageously is removed from the solventmixture to leave behind a solvent solution comprising a vinyl chloridepolymer, a solvent and a plasticizer.

It will be observed that the supplementary flocculating agent has beenflocculated out of the solvent mixture. In order to recover finally anessentially pure resin, the plasticizer and the solvent and non-solventsfor reuse, it becomes necessary to remove the acid used to causeflocculation. This may be accomplished by adding a constituent such as,for example, calcium hydroxide, having a basic pH value, to neutralizethe acid. The calcium hydroxide is added to the solvent mixture severalminutes, e.g., on the order of ten minutes after the addition of theacid and heating of the contents of the tank 42. Unexpectedly, the basicmaterial, e.g., calcium hydroxide, has a dual function. Not only does itadvantageously neutralize the acidic constituent, but it alsoaccelerates the flocculation process by about 75%.

Surprisingly, the calcium carbonate which may be present as a fillerapparently does not neutralize the acid constituent prematurely. Sinceonly a small amount of acid is used as compared to the calcium carbonatepresent, it would appear to be expected that the calcium carbonate wouldneutralize the acid before the flocculation would begin to occur.

The solvent mixture is then moved along a line 51 by a pump 52 and intofilters 53--53. It is well known in the art to filter a solvent mixtureto remove colloids. The principles of this invention which includeflocculation render filtration unnecessary. However, filtration is aworthwhile supplement to the flocculation to still further refine thesolvent mixture. Moreover, filtration may be used to remove effectivelylarge curds from the solvent mixture. It should be understood that othertechniques such as centrifuging or settling could be used instead offiltering.

The filters 53--53 are supplied along a line 54 from a supply tank 56through a valve 57. The supply tank 56 includes a filter medium such asa suspension of diatomaceous earth in MEK solution which is stirred byan agitator 55 and is moved into the filters 53--53 and deposited as acoating.

Typically, each filter element includes a support such as a perforatedmetal base plate and a fine-mesh metal or fabric material on topthereof. Atop the mesh, a coating of particulate filter material such asdiatomaceous earth is built up, advantageously to a thickness of about a16th of an inch, or 1.0 to 1.5 pounds of diatomaceous earth for every 10square feet of filter surface.

The filters 53--53 remove the floc. In a preferred embodiment, the flocis settled out in the tank 42 with the solvent mixture decanted out thetop. The removal of the floc at the bottom of the tank 42 savesadvantageously the filters 53--53.

The use of the heater 43 facilitates high filter flow rates bymaintaining the solvent mixtures at a temperature, for example, in therange of 30° C. to 65° C., at which the viscosity does not become toogreat. Likewise, the filters 53--53, when used, may be heated byfacilities (not shown).

The filter system is rechargeable when the diatomaceous earth isparticle-saturated. This is accomplished by shutting off the tank 42 atthe valve 52 and by flushing the system with solvent through thecharging line 54. Spent diatomaceous earth, residual solvent and otherfiltered constituents are removed from the filters 53--53, moved througha valve 58, along a line 59 and into a recovery tank 61.

Following the flocculation and the optional filtering or centrifugingstep, the next step of the process which embodies the principles of thisinvention includes treating the solvent mixture to precipitate out thePVC. The solvent mixture is moved along a line 62 at room temperatureinto a precipitator 63 having cooling facilities 64 in a preferredembodiment. An essentially pure uncontaminated PVC, is precipitated outof the solvent mixture, advantageously as powdery granules, by adding asubstantially equal volume of a suitable non-solvent, or precipitatingagent for the vinyl chloride polymer, which may be, for example, methylalcohol (methanol) or a methanol-MEK azeotrope.

The non-solvent is moved from a storage tank 66 along a line 67 andthrough a valve 68 into the precipitator 63. The non-solvent and thesolvent mixture now in the tank 63 are subjected to a stirring action byan agitator 70. The temperature of the solvent solution in theprecipitator is cooled advantageously to approximately 25° C. bysuitable cooling apparatus such as, for example, the cooling facilities64 shown in FIG. 2. Cooling at this stage renders the PVC less solublein the solvent, e.g., MEK and hence more readily precipitable. Thesolvent, e.g., MEK and the non-solvent, e.g., methanol are miscible insubstantially all proportions, and as noted, the non-solvent, e.g.,methyl alcohol also dissolves advantageously the plasticizer.

Care also must be used to select a precipitating agent or non-solventwhich precipitates out as high a percentage as possible of the dissolvedPVC present. Methyl alcohol (methanol) or an MEK-methanol azeotrope hasbeen found to be an effective non-solvent for the PVC. When added sothat the methanol content is in a 50:50 ratio by volume to the solvent,e.g., MEK, solution, better than 99% of the PVC present is precipitated.A 40:60 methyl alcohol-MEK mixture precipitates 97-98% of the PVC, whichis an acceptable, although somewhat less efficient, recovery factor. Ithas been found that methanol in excess of the 50:50 ratio does not yieldsignificantly more PVC. When using a recycled azeotrope of MEK-methanolsystem, it has been found that 2.7 parts of azeotrope to one part MEKare required to precipitate efficiently the PVC.

The precipitator contents are discharged through a line 69 into aseparator 71 where the PVC precipitate may be moved onto a vacuum filterbed 72. Advantageously, the bed 72 includes a moving wire mesh belt 73which transports the particles across the vacuum bed where the solventand precipitating agents are removed. The particles are fed to a chute74 which leads into a resin dryer 75. The residual solvent and theprecipitating agents are here removed, and dried. Granular,substantially pure, PVC is collected in a bin 76 and is ready to bereused in insulating and sheathing material for wire and cable.

It was mentioned earlier that the acid used in the flocculating step maybe removed by the addition of a neutralizing agent subsequent to theaddition of the acid itself to the solvent mixture. In the alternative,the solvent solution which includes the PVC solvent and non-solvent, theplasticizers and the acid may at this time in the process be passed overa neutralizing bed, e.g., a calcium hydroxide bed.

The solvent solution is collected in a holding tank 77 which suppliesthe solution along a line 78 to a boiler 79. In the boiler 79, theelevated temperature causes the solvent and non-solvent to be boiled offalong the line 81 to a fractional distillation tower 82. The remainingplasticizers are pulled over a line 83 to a vacuum still 84 where theplasticizers may be recovered individually.

In telephone wire and cable products, the plasticizers typically aredialkyl phthalates in which the alkyl groups contain between 6 and 13carbon atoms. Another class of plasticizers commonly used are adipateswhich are made from adipic acid and alcohol. The adipates will alsodissolve in the non-solvents described above. The phthalates andadipates are generally high boiling point viscous oils boiling at about200° C. and above.

Of the phthalate plasticizers, the common ones are di-2-ethylhexylphthalate (DOP), boiling point at 5 milimeters, 185° C.; diisooctylphthalate (DIOP), boiling point at 5 millimeters, 195° C.; diisodecylphthalate (DIDP), boiling point at 5 millimeters, 248° C.; ditridecylphthalate (DTDP), boiling point at 5 millimeters, 300° C.;n-hexyl-n-decyl phthalate (61OP), boiling point at 247° C.; andn-octyl-n-decyl phthalate (81OP), boiling point 261° C. Another commonplasticizer family are phosphates such as tricresyl phosphate, boilingat about 410° C. All of the aforementioned plasticizers may be recoveredby the principles of the methods of this invention.

In the fractional distillation tower 82, the solvents and non-solventsare separated according to their respective boiling points. For example,in the situations where MEK and methanol are employed as the solvent andnon-solvent, respectively, MEK and an azeotrope of methanol and MEK, asopposed to pure methanol, are recovered and reusable as the solvent andnon-solvent. The higher boiling point MEK, condenses in the lower regionof the fractional distillation tower 82 and is either removed to anauxiliary storage tank 86 via a line 87 or returned over a line 88 tothe MEK storage tank 28. The MEK-methanol azeotrope, having a lowerboiling point, is removed at the upper region of the tower 82 and iseither moved through a line 91 and collected in an auxiliary tank 92 oris returned via line 93 to the storage tank 66. The MEK in the auxiliarystorage tank 86 is reheated in a heater 96 before reuse.

It will be recalled that acetates other than cellulose acetates may beused as a flocculating agent. If so, the other acetates known to besuitable for this purpose are liquid acetates and may be directed alongthe line 88 together with the solvent to the storage tank 28. Thisavoids the necessity of substantial replenishment of the flocculatingagent.

In general, plasticized or unplasticized scrap vinyl chloride polymerscapable of being dissolved may be solvent-reclaimed by the process ofthe present invention. The PVC suitable for reclaiming by the practiceof this invention includes at least all general purpose resins embracedwithin the industry specification ASTM D1755-60T.

The recovered PVC resin advantageously has been found to have asignificantly more peaked molecular weight distribution curve than thatof virgin PVC's. The distribution curve for virgin and PVC recycled by aprocess embodying the principles of this invention are shown in FIG. 3.The molecular weight distribution may effect the processing qualities ofresins. A high molecular weight increases processing difficultieswhereas low molecular weight resins may have less than desired chemicalor physical properties. A resin having a molecular weight distributionof the recovered resin has less than normal high weight distribution andtherefore is easier to process, and has fewer low weight moleculesthereby yielding improved physical properties.

The apparatus 20 which embodies the principles of this inventionincludes facilities for conserving solvent. Condensing equipment whichreceives solvent and precipitant vapors developed at numerous stages inthe process and condenses them for reuse is not shown in FIG. 2 for sakeof clarity. However, it is to be understood that condensing apparatusmay be associated with the solution tank 26, the screen 36, theprecipitator 63, and the vacuum filter 73, as well as at other locationsin the system where solvent or other vapors accumulate.

It has been determined that a number of binary systems comprisingsolvents and precipitating agents may be used commercially in recoveringpolyvinyl chloride. The principal difference between the many binarysystems which could be employed involves the volumes of theprecipitating agent required to yield a thoroughly dried resin of highporosity. Dissolved PVC resin can be precipitated from the solutioncomprising any solvent provided the non-solvent for the PVC is ofsufficiently different polarity and as long as it is completely misciblein the solvent.

The binary system should be designed so that the solvent which is avolatile organic liquid has a boiling point sufficiently different fromthat of the non-solvent to permit the economical separation and recoveryof the solvent and the non-solvent by the fractional distillationthereof.

It has been found that THF and cyclohexanone are most suitable solventsfor PVC and that they solvate virgin PVC resin readily and at roomtemperature (25° C.). No heat is required to affect a homogeneoussolution of low viscosity. Although THF appears to be preferred, it iscostly.

The MEK requires mild heating to approximately 40° C. to solvate PVCresin. Once in solution, however, cooling to moderate temperatures ofapproximately 20° C. does not cause precipitation. High PVCconcentrations promote gel formation when agitation is not continuous.The use of MEK as the solvent yields a high quality resin withoutsolvent occlusion. Cyclohexanone, as well as MEK, is especially suitablefor commercial recovery processes because of its low cost. Once solvatedin cyclohexanone, it has been found that the PVC does not precipitatenor cause gelling on reduction of temperature nor does the solutionbecome especially viscous. With this solvent, the polarity of theprecipitating agent is more important than with THF or MEK.

One difficulty encountered with cyclohexanone concerns the drying of thePVC resin after precipitation. Cyclohexanone tends to plasticize the PVCresin, yielding a soft material unless large volumes of precipitant (30per part of cyclohexanone, for example) are used. This problem can becircumvented by washing the freshly precipitated resin with pureprecipitant. This removes the cyclohexanone from the resin and permitsthorough drying to yield desirably a powdery, dry PVC resin.

Although not required, it has been found that a mild heating of DMF isadvantageous in dissolving the PVC resin. Alcoholic precipitants causesubstantial occlusion of DMF and incomplete drying of precipitated resin(110 percent recovery). It has been found that washing the wetprecipitated resin with fresh precipitant effectively removes residualDMF and permits complete drying thereby yielding dry resin in porousform as opposed to the rigid material recovered after the regularprecipitation sequence.

Mesityl oxide has been investigated to determine its dissolution effectupon PVC and irradiated PVC. As with the other hereinbefore mentionedfour solvents, mesityl oxide dissolves PVC but not the irradiated PVC.The PVC resin is recoverable as a moderately hard precipitant with theaddition of methanol.

In general, the precipitating agent non-solvent should be selected so asto dissolve all the plasticizers that may be encountered in the scraprecovery process. Substantially, all alcohols will precipitate PVC fromany PVC solvent. The preferred alcohols, however, are those which havethe characteristics of low boiling point, low cost and low toxicity.Precipitating agents that are either highly polar or highly nonpolar arecandidates for the process.

An alternative system for reclaiming PVC is to employ THF as a solventand isopropyl alcohol as the precipitant. The boiling point of THF is65° C. and that of isopropyl alcohol is 80° C., thus providing afavorable separation for fractional distillation.

The following examples are illustrative of reclamation processing inaccordance with the principles of this invention. All parts andpercentages are by weight unless otherwise indicated.

EXAMPLE I

Six hundred seventy-four grams of cyclohexanone solvent were heated to69° C. and were used to treat a 100.9 gram charge of PVC insulated scrapwire (e.g. 20-26 gauge) and PVC jacket cable comprising mixed alkylphthalate plasticizer that had been chopped into approximatelyone-fourth inch lengths. The PVC was dissolved in the solvent and 69.6grams of coarse gross solids were filtered out. The resultant filtratewas heated to 151° C. accompanied by agitation. At that point, 1.1 ml ofconcentrated HCl was added to flocculate suspended particulates. After 2minutes, 2.25 grams of calcium hydroxide were added. The application ofheat and agitation was discontinued to allow the floc to settle. Theclear supernatant liquid was decanted from the 10.7 grams of floc. Twothousand ml of methanol were added to precipitate out the PVC. The PVCwas filtered off through filter paper and was washed in 1000 mlmethanol. The PVC was then dried in a vacuum oven for several hours,yielding 16 grams of essentially pure resin. The filtrate was collectedand evaporated to yield 5.1 grams of mixed alkyl phthalate plasticizer.

EXAMPLE II

A charge of 34.9 grams of PVC wire and cable scrap which had beenchopped into approximately 1/4 inch lengths was mixed with 235 grams ofMEK. Approximately 0.4 gram of cellulose acetate was added. The mixturewas refluxed until the PVC had dissolved and then filtered to remove thegross solids such as metal and other insoluble components of scrap. Theresulting opaque colloidal liquid suspension was heated to reflux withagitation and 0.5 ml of conc. HCl was added. This was followed withinone minute by the addition of 0.6 gram of calcium hydroxide. A largecurd floc formed. The application of heat was discontinued and the flocsettled. The clear supernatant liquid comprised mainly of PVC, MEK andplasticizer was decanted. Added to the decanted solution to causeprecipitation of the PVC were 810 ml of the MEK-methanol azeotrope. ThePVC was filtered out on filter paper and dried for several hours in avacuum oven to yield 6.5 grams of an essentially pure resin. Thefiltrate, comprised mainly of MEK, methanol and plasticizer wassubjected to heat and air to boil off the MEK and methanol yielding 2.1grams of mixed alkyl phthalate plasticizer.

EXAMPLE III

A charge of 34.9 grams of PVC wire and cable scrap which had beenchopped into approximately 1/4 inch lengths was mixed with 257 grams ofMEK and approximately 0.5 gram of cellulose acetate was added thereto.The mixture was refluxed with the application of heat and agitationuntil the PVC had dissolved. The mixture of undissolved solids,colloidally suspended material, and solution of PVC, plasticizers andcellulose acetate was filtered to remove the coarse undissolved solids.The supernatant fluid was heated to boiling and 0.5 ml of HCl was addedwhich resulted in immediate flocculation of the suspended particles. Theapplication of heat and agitation was discontinued to allow the floc tosettle and the clear supernatant, comprised mainly of PVC, plasticizersand MEK, was decanted from the floc. The PVC was precipitated out ofsolution by the addition of 450 ml methanol. Both the PVC solution andthe methanol were at room temperature. The particulate PVC was filteredout and dried in a vacuum oven to yield 6.5 grams of resin. Thesupernatant was evaporated off to yield 2.1 grams of mixed alkylphthalate plasticizers.

EXAMPLE IV

A charge of scrap PVC wire and cable was mixed with MEK and celluloseacetate and treated essentially as in Example III. The only differencewas that in the flocculation step, gaseous hydrogen chloride was bubbledinto the PVC compound - MEK filtrate. This caused immediateflocculation.

EXAMPLE V

A charge of 34.0 grams of scrap PVC wire and cable chopped into 1/4 inchlengths was added to 230 grams MEK. The PVC was dissolved and the coarsesolids were removed as in the preceding example. The cloudy fluid fromthe coarse filtration was heated to boiling and 0.5 ml conc. HCl wasadded followed by the addition of 0.6 gram of calcium hydroxide. Coarsefloc formed immediately. The mixture was immediately removed from theheat to allow the floc to settle. The clear liquid was decanted and 450ml methanol were used to precipitate the PVC resin. The resin was driedand 6.1 grams were collected; 2 grams of the mixed alkyl phthalateplasticizer recovered.

EXAMPLE VI

A charge of 40.0 grams of scrap PVC wire and cable was added to 266grams of THF with 0.5 gram cellulose acetate. The PVC dissolved in about30 minutes. At this point the coarse, undissolved components werefiltered out. The remaining opaque liquid was heated to reflux and 0.5ml conc. HCl was added. Then, 0.6 gram calcium hydroxide was addedcausing the immediate formation of a large curd floc. The mixture wasallowed to cool and settle for 75 minutes. The clear solution wasdecanted and 450 ml of isopropanol were added. The volume of solutionwas reduced by evaporation and the PVC resin precipitated out. The PVCthat was filtered out was dried to yield 7.4 grams. Then the solvent andnon-solvent were boiled off from the filtrate yielding 2.5 grams ofmixed alkyl phthalate plasticizer.

TEST RESULTS

A PVC resin recovered in accordance with the principles of the methodsof this invention together with 27 parts of recovered mixedplasticizers, per 100 parts resin, were compounded with 5 parts ofdiphenyl phthalate, per 100 parts of resin, 0.4 parts of wax, per 100parts of resin, 0.4 parts of dibasic lead stearate, per 100 parts resin,and 7 parts of dibasic lead phthalate, per 100 parts resin, to yield anextrudable material suitable for an insulating compound. The propertiesof the compound are:

                  TABLE I                                                         ______________________________________                                        Specific Gravity     1.3 - 1.4                                                Tensile Strength     > 3500                                                   Ultimate Elongation  > 250%                                                   Thermal Stability    > 10 minutes                                             Tear Resistance      > 1000 #/in.                                             Shear Resistance     > 2000                                                   Volume Resistivity Wet                                                                             > 10.sup.16                                              Dry                  > 10.sup.16                                              Dielectric Constant  3.7 - 3.8                                                ______________________________________                                    

EXAMPLE VII

Same as Example III except that poly (vinyl isobutyl ether) was used inplace of cellulose acetate.

EXAMPLE VIII

Same as Example III except that poly (methyl methacrylate) was used inplace of cellulose acetate.

EXAMPLE IX

Same as Example III except that polystyrene was used in place ofcellulose acetate.

EXAMPLE X

Same as Example III except that poly (vinyl acetate) was used in placeof cellulose acetate.

EXAMPLE XI

Same as Example III except that ethyl acetate was used in place ofcellulose acetate.

EXAMPLE XII

20 grams of PVC extruder purgings and 0.5 gram of ethylene vinyl acetatewere dissolved in 400 grams of methyl ethyl ketone by refluxing the wellstirred mixture for 1 hour. Then 4 ml of concentrated hydrochloric acidwere added to the solution and the reflux continued for another 20minutes. As the solution cooled 4 grams of flocculated material settledout and were removed.

500 ml of methanol were added and 11 grams of resin precipitated. Thesolution was evaporated and 3 grams of mixed alkyl phthalates wererecovered.

EXAMPLE XIII

100 grams of chopped scrap cable and wire were stirred with 400 grams ofMEK and 20 grams of ethyl acetate. The solution was stirred and refluxedfor 1 hour and then 4 ml of concentrated hydrochloric acid were added.Reflux was continued for another 20 minutes. The same procedure wasfollowed as was given in Example I.

EXAMPLE XIV

Same as Example XIII except that isopropyl acetate was used instead ofethyl acetate.

EXAMPLE XV

Same as Example XIII except that butyl acetate was used instead of ethylacetate.

EXAMPLE XVI

Same as Example XIII except that isoamyl acetate was used instead ofethyl acetate.

It is to be understood that the above described arrangements are simplyillustrative of this invention. Other arrangements may be devised bythose skilled in the art which will embody the principles of theinvention and fall within the spirit and scope thereof.

What is claimed is:
 1. A method of recovering a reusable essentiallypure vinyl chloride polymer resin from a scrap polymer mixture whichcomprises plasticized polyvinyl chloride and insoluble additives, whichincludes the steps of:contacting a polymer mixture which comprisesplasticized polyvinyl chloride and insoluble additives with a solventfor vinyl chloride polymers to form a solvent mixture comprising asolvent solution of dissolved vinyl chloride polymer and plasticizersand other insoluble additives; treating the solvent mixture with an acidwhich is selected from the group consisting of an inorganic acid and aninorganic acid solution and which is substantially soluble in thesolvent in the presence of a flocculating agent which is selected fromthe group consisting of liquid monomeric esters, polystyrene, polyethylmethacrylate, poly (vinyl isobutyl ether), polyvinyl acetate andethylene vinyl acetate to flocculate and remove the suspended additives;and treating the solvent solution with a non-solvent which is misciblewith the solvent in substantially all proportions and which is a solventfor the plasticizer to precipitate an essentially pure vinyl chloridepolymer resin therefrom.
 2. The method of claim 1, wherein the solventis selected from the group consisting of tetrahydrofuran, methyl ethylketone or dimethyl formamide and the acid is an acid selected from thegroup consisting of nitric acid, sulfuric acid, and hydrochloric acid,the liquid monomeric ester is selected from the group consisting ofethyl acetate, propyl acetate, isopropyl acetate, isoamyl acetate,pentyl acetate, butyl acetate and a mixture comprising any of theforegoing acetates, and the non-solvent is selected from the groupconsisting of methanol, isopropanol, n-butanol, or an azeotrope ofmethyl ethyl ketone and methanol.
 3. The method of claim 1, wherein thescrap polymer mixture is a scrap conductor scrap material and theflocculating agent is selected from the group consisting of liquidmonomeric esters, polystyrene, polymethyl methacrylate, poly (vinylisobutyl ether) and polyvinyl acetate.
 4. The method of claim 1, whereinthe scrap polymer mixture is a scrap plastic scrap material and theflocculating agent is selected from the group consisting of polystyrene,polymethyl methacrylate, poly (vinyl isobutyl ether), polyvinyl acetateand ethylene vinyl acetate.
 5. A method of separating metal, polyvinylchloride and plasticizer from scrap conductor material containing metaland plasticized polyvinyl chloride which also includes insolubleparticulate matter comprising pigments and fillers, comprising the stepsof:dissolving the polyvinyl chloride in methyl ethyl ketone at atemperature above ambient to form a solvent mixture containing a solventsolution comprising dissolved polyvinyl chloride, entrained particulatematerial and undissolved metal; separating the undissolved metal fromthe solvent mixture; treating the solvent mixture with an acid which isselected from the group consisting of an inorganic acid and an inorganicacid solution which is substantially soluble in the solvent in thepresence of a flocculating agent selected from the group consisting ofliquid monomeric esters, polystyrene, polymethyl methacrylate, poly(vinyl isobutyl ether) and polyvinyl acetate to cause a flocculation ofthe pigments and fillers; treating the solvent solution to precipitateout the polyvinyl chloride by adding methanol in which the polyvinylchloride is substantially insoluble and which produces fine-grainedunagglomerated polyvinyl chloride particles, the methanol being misciblein all proportions with the methyl ethyl ketone, being a solvent for theplasticizer in the resin material, and having itself a boiling pointsignificantly different from both the methyl ethyl ketone and theplasticizer; removing the polyvinyl chloride particles, andfractionating the remaining solvent solution to recover separately thesolvent, an azeotrope of the methanol and methyl ethyl ketone and theplasticizer.
 6. A method of separating fillers, metal salts, andinsoluble pigments from a vinyl chloride polymer scrap material, whichincludes:contacting a vinyl chloride polymer scrap material with asolvent which is a solvent for vinyl chloride polymer and plasticizersto form a solvent mixture; and contacting the solvent mixture with anacid which is selected from the group consisting of an inorganic acidand an inorganic acid solution and which is substantially soluble in thesolvent in the presence of a flocculating agent which is selected fromthe group consisting of liquid monomeric esters, polystyrene, polymethylmethacrylate, poly (vinyl isobutyl ether) and polyvinyl acetate, toflocculate the fillers, metal salts and insoluble pigments.
 7. A methodof recovering an essentially pure plasticized polyvinyl chloride mixturefrom a scrap polyvinyl chloride material, which includes the stepof:contacting a scrap polyvinyl chloride material with a solvent whichis a solvent for a vinyl chloride polymer and plasticizers and which isselected from the group consisting of methyl ethyl ketone,tetrahydrofuran or dimethyl formamide to form a solvent mixture;flocculating out insoluble additives by treating the solvent mixturewith an acid which is selected from the group consisting of nitric acid,sulfuric acid, and hydrochloric acid in the presence of a flocculatingagent which is selected from the group consisting of liquid monomericesters, polystyrene, polymethyl methacrylate, poly (vinyl isobutylether), and polyvinyl acetate; and evaporating the solvent to recover anessentially pure plasticized polyvinyl chloride.
 8. The method of claim7, wherein the scrap material is a scrap conductor scrap material andthe liquid monomeric ester is selected from the group consisting ofethyl acetate, propyl acetate, isopropyl acetate, pentyl acetate, andbutyl acetate.
 9. The method of claim 7, wherein the scrap charge is ascrap plastic scrap material, and the flocculating agent is selectedfrom the group consisting of polystrene, polymethyl methacrylate, poly(vinyl isobutyl ether), polyvinyl acetate and ethylene vinyl acetate,and the flocculating agent is added to the solvent mixture prior totreating the mixture with an acid.
 10. An essentially pure polyvinylchloride resin recovered from a scrap material in accordance with themethod of claim
 1. 11. An essentially pure plasticized polyvinyl resinrecovered from a scrap material in accordance with the method of claim7.